Car body formed by friction stir welding

ABSTRACT

A raised portion  32  is provided on an upper face of an end portion of a plate  31  which forms one side of a frame member  30.  An end portion of a plate  41  of another frame member  40  is abutted with the plate  31  of the frame member  30.  The frame members  30  and  40  are aluminum alloy extruded frame members and the directions of extrusion of the two frame members are orthogonal. A welding padding is carried on an upper face of the plate  41  of the frame member  40.  Under this condition, a rotary tool is inserted from above and a friction stir welding is carried out. Accordingly, the padding serves the same function on the plate  41  as the raised portion  32  on the plate  31,  so that a good welding can be carried out.

[0001] This application is a Divisional application of Ser. No.09/927,549, filed Aug. 13, 2001, which is a Divisional application ofSer. No. 09/404,651, filed Sep. 24, 1999.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a method of friction stirwelding which may be used in welding, for example, aluminum alloymaterial frame members; and, more particularly, the invention relates toa method of friction stir welding which may be used, for example, in acase where the heights of portions of two abutting aluminum alloy framemembers to be joined by welding differ.

[0003] As disclosed in Japanese application patent laid-open publicationNo. Hei 9-309164 (EP 0797043A2), a friction stir welding method is amethod in which, by rotating a round rod (called a rotary tool) which isinserted into a welding portion of two abutting frame members to besubjected to welding and moving the rotary tool along a welding line;the welding portion of the two frame members to be subjected to thewelding is thermoplastically heated so as to be plastically fluidizedand welded.

[0004] The rotary tool comprises a small diameter portion to be insertedinto the joint of the welding portion and a large diameter portion whichis positioned outside of the small diameter portion. The small diameterportion of the rotary tool and the large diameter portion of the rotarytool are positioned on the same axis.

[0005] The large diameter portion of the rotary tool and the smalldiameter portion of the rotary tool are simultaneously rotated. Thewelding according to the friction stir welding method is applied to anabutting portion and an overlapping portion of the two frame members tobe subjected to the welding, which members are made of aluminum alloymaterials, for example.

[0006] Further, to the welding portion of one frame member to besubjected to the welding, there is provided a raised portion whichprotrudes in a direction toward the large diameter portion of the rotarytool. This raised portion of the frame member is provided integrallywith an end portion in a width direction of a hollow extruded framemember.

[0007] The above-stated raised portion provides material for burying agap which is formed between the two hollow extruded frame members duringwelding. When a side of the raised portion of the frame member forms anouter face of a product, for example, an outer side of a car body of arailway vehicle, after the welding the remnants of the raised portion ofthe frame member are cut off.

[0008] When the above-stated raised portion is provided on the extrudedframe member, the raised portion can be provided to extend along anextruding direction. However, the raised portion of the frame member cannot be provided at an end portion of the extruded portion; in otherwords, the raised portion of the frame member can not be provided at arectangular direction against the side of the raised portion. As aresult, when the extruded frame members are arranged to be orthogonal toeach other and the end portions of the extruded frame members aresubjected to welding according to a friction stir welding method, araised portion exists at an end portion of one extruded frame member,however a corresponding raised portion does not exist on the otherextruded frame member at the welding portion.

[0009] Accordingly, it is considered that a good welding of the twoextruded frame members can not be carried out, because one of theextruded frame members does not have a raised portion at the weldingportion.

[0010] The above stated fact applies generally to a case in which theheight of the surfaces in the width direction of the two extruded framemembers of the welding portion differ from each other; in other words,for a case in which the height of the surface in the width direction ofone frame member differs from the height of the surface in the widthdirection of the other frame member. The typical situation is that theheight of the surface in the width direction of the one frame member ishigher or lower than the height of the surface in the width direction ofthe other frame member.

SUMMARY OF THE INVENTION

[0011] An object of the present invention is to provide a method offriction stir welding wherein a good welding can be obtained even whenthe height of the surfaces of the two members at the welding portiondiffer.

[0012] The above stated object can be attained when the height of thesurfaces of the two members at the welding portion differ, by welding apad on the surface of a member at a low side, followed by friction stirwelding of the welding portion of the two members.

[0013] Further, the above statement that “the heights of the surfaces ofthe two members at the welding portion differ” refers to a case in whichthe above-stated surface side, for example, extends toward an upperportion or a lower portion; however, when the rotary tool is standard asa determination of a position, it means that the distance from therotary tool to the surface of the welding portion differs, for example.The above reference to “the member being on the low side” indicates amember which is at a larger distance from the rotary tool.

BRIEF DESCRIPTION OF DRAWINGS

[0014]FIG. 1 is a longitudinal cross-sectional view showing a weldingportion of two frame members to be subjected to friction stir weldingaccording to the present invention and corresponds to a cross-sectionalview taken along line I-I in FIG. 6;

[0015]FIG. 2 is a perspective view of the vicinity of a welding portionto be subjected to the welding of the two frame members of FIG. 1;

[0016]FIG. 3 is a cross-sectional view of a rib of the frame membertaken along line III-III in FIG. 1;

[0017]FIG. 4 is a longitudinal cross-sectional view of a welding portionof another part of the two frame members according to the presentinvention and corresponds to a cross-sectional view taken along lineIV-IV in FIG. 6;

[0018]FIG. 5 is a cross-sectional view showing the state of the weldingportion after welding in which friction stir welding has been carriedout on the two frame members of FIG. 4;

[0019]FIG. 6 is a side view showing a car body of a railway vehicle onwhich the friction stir welding is carried out according to the presentinvention;

[0020]FIG. 7 is a side view showing another car body of another railwayvehicle on which the friction stir welding is carried out according tothe present invention;

[0021]FIG. 8 is a cross-sectional view of the two frame members takenalong line VIII-VIII in FIG. 7; and

[0022]FIG. 9 is a cross-sectional view showing a further car body of afurther railway vehicle on which the friction stir welding is carriedout according to the present invention and which corresponds to theembodiment shown in FIG. 8.

DESCRIPTION OF THE INVENTION

[0023] A friction stir welding method according to the present inventionas applied to a car body of a railway vehicle will be explained withreference to FIG. 1 to FIG. 6.

[0024] As seen in FIG. 6, the side structure of the body 20 of a railwayvehicle is constituted by combining plural aluminum alloy extruded framemembers 30, 40 and 50. The extruding direction of the extruded framemembers 30, which are made of aluminum alloy materials and are arrangedon either side of a doorway 21, and the extruding direction of theextruded frame members 30 disposed between a window 25 and another framemember 30 disposed adjacent to the doorway 21, extend in the verticaldirection as seen in FIG. 6.

[0025] The extruding direction of the extruded frame members 40, whichare made of aluminum alloy materials and are disposed below a window 25,extends in a lateral direction as seen in FIG. 6. In other words, theextruding direction of the extruded frame members 30 and the extrudingdirection of the extruded frame members 40 are orthogonal to each other.The extruding direction of the extruded frame member 50, which is madeof aluminum alloy materials and is disposed at an upper portion of thecar body above the doorway 21, also extends in a lateral direction asseen in FIG. 6. The reference numeral 28 indicates a bougie frame of thecar body. These members are welded together using a friction stirwelding method and an ordinary MIG welding method.

[0026] Referring to FIG. 4 and FIG. 5, the friction stir welding of theextruded frame members 30 to each other in which the extrudingdirections are the same will be explained. The friction stir welding ofthe extruded frame members 40 is carried out in a similar manner.

[0027] The extruded frame member 30 (similarly to the frame members 40and 50) comprises a flat plate 31 forming an outside surface of the carbody and in an inside surface of the car body, and plural ribs 33 arearranged on the inside surface of the flat plate 31. The rib 33 isprovided to extend along the extruding direction of the extruded framemember 30 (similar to the frame members 40 and 50).

[0028] At one end (an end portion where the frame members 30 abut eachother) in the width direction (the direction orthogonal to the extrudingdirection of the extruded frame member) of the extruded frame member 30,there is a raised portion 32 on the inside of the car body (the rib 33side).

[0029] The height of the raised portion 32 of the frame member 30 isshown as h. A face 32 b formed by the end portion of the plate 31 andthe end portion of the raised portion 32 is arranged to be substantiallyorthogonal to an upper face or an apex 32 c of the raised portion 32 ofthe plate 31 of the frame member 30.

[0030] Accordingly, when two extruded frame members 30 are abutted, thefaces 32 b of the end portions of the plates 31 of the frame members 30come into close contact with each other. However, this is an ideal case.The abutted portion actually is said to have an I-shaped groove formstructure.

[0031] When friction stir welding is carried out on two abutting framemembers 30, in order to not create a gap between the two frame members30, (to maintain the gap at a predetermined value), the extruded framemembers 30 and 30 are restrained or clamped on a stand 60. For thispurpose, each extruded frame member 30 is mounted on the stand 60 withthe raised portion 32 of the plate 31 directed upward. Further, thewelding portion formed by the ends of the extruded frame members 30 isdisposed in close contact with the stand 60, which is made of a steelmaterial.

[0032] A rotary tool 70, which is a tool for carrying out the frictionstir welding of the two frame members 30, is inserted into the weldingportion from above. The rotary tool 70 is constituted by a largediameter portion 71 and a small diameter portion 72 disposed at the tipend (a low end) of the large diameter portion 71.

[0033] A boundary surface 73 (formed by an outer peripheral surface ofthe large diameter portion 71 of the rotary tool 70) between the largediameter portion 71 and the small diameter portion 72 of the rotary tool70 has an arc shape which is recessed into the large diameter portion71. The small diameter portion 72 has a screw structure.

[0034] During the friction stir welding, the raised portion of the framemember 30 extends into the recess formed by the boundary surface 73 (theouter peripheral portion of the large diameter portion 71 of the rotarytool 70). In other words, the boundary surface 73 is recessed by anamount which is intermediate (a length is a protrusion depth h) betweenthe apex 32 c of the raised portion 32 and the face 31 b (a face of anon-raised portion) at the inner surface of the plate 31 of the framemember 30.

[0035] The friction stir welding is carried out by rotating the rotarytool 70 and inserting it into the welding portion of the two extrudedframe members 30; and, while continuing the rotation, moving the rotarytool 70 along a welding line between the two extruded frame members 30.The axial center line of the rotary tool 70 is positioned in alignmentwith the end face 32 b of the extruded frame member 30.

[0036] Further, the axial center of the rotary tool 70 is inclinedrelative to the moving direction of the rotary tool 70. Accordingly, thefront end of the large diameter portion 71 of the rotary tool 70 in thedirection of movement is positioned to an outer face side (in FIG. 4, anupper portion from the apex 32 c) of the apex 32 c of the raised portion32 of the frame member 30. A rear end of the large diameter portion 71of the rotary tool 70 is positioned to engage the raised portion 32 (toa depth indicated by a line 32 d) of the frame member 30. In otherwords, during welding, the rear end of the large diameter portion 71 ofthe rotary tool 70 extends into the raised portion 32 to a positionbetween the apex 32 c of the raised portion 32 and an extension line ofthe face 31 b of the plate 31 of the frame member 30. The above-statedterms “front” and “rear” are defined with reference to the movingdirection of the rotary tool 70.

[0037] The relationships between the sizes of the respectiveconstructive parts will be explained. The width WI of the apexes 32 c ofthe raised portions 32 of the frame members 30 when the two raisedportions 32 are abutted is larger than the diameter d of the smalldiameter portion 72 of the rotary tool 70, but is smaller than thediameter D of the large diameter portion 71 of the rotary tool 70.However, the width W1 of the apex 32 c also can be formed to be largerthan the diameter D of the large diameter portion 71 of the rotary tool70.

[0038] A width W2 of the base portion formed by two raised portions 32is larger than the diameter D of the large diameter portion 71 of therotary tool 70. The height H of the small diameter portion 72, when theraised portion of the frame member 30 extends into the recess formed bythe boundary surface 73 of the rotary tool 70, has a size such that thetip end of the small diameter portion 72 of the rotary tool 70approaches the stand 60 during welding.

[0039] For example, the distance between the outer face 31 c of theplate 31 and the tip end of the small diameter portion 72 of the rotarytool 70 is approximately 0.1 mm during welding. In other words, thedimensions of the rotary tool and the movement thereof are set toprevent the tip end of the small diameter portion 72 of the rotary toolfrom contacting the stand 60 during welding. The surface of the apex 32c of the raised portion 32 and the face 31 b of the plate 31 of theframe member 30 are joined by an inclined face 32 e.

[0040] After the two extruded frame members 30 have been fixed to thestand 60, the friction stir welding is carried out. The apparatus forrotating the rotary tool 70 has rollers which move to accompany movementof the rotary tool 70 along the weld. The rollers provided on the rotarytool 70 are arranged on a right side and a left side at a front portionand a rear portion of the rotary tool 70 in the direction of movement ofthe rotary tool 70 along the weld. When the rotary tool 70 is insertedinto the weld portion of the two extruded frame members 30, the rollerscontact the faces 31 b of the two extruded frame members 30 and the twoextruded frame members 30 are thereby pressed against the stand 60.

[0041]FIG. 5 shows a state or a condition of the two extruded framemembers 30 and 30 after completion of the friction stir weldingaccording to the present invention. The material of the raised portion32 of the extruded frame member 30 into which the large diameter portion71 has been inserted is supplied to a gap which is formed between thetwo abutting frame members 30 and flows out to the outside face of thetwo extruded frame members 30 as a facet. Also, part of the materialremains as a fin on either edge of the raised portion 32. Accordingly, acentral portion of the two raised portions 32 of the two extruded framemembers 30 forms a recessed portion 35. The gap between the two framemembers 30 is filled by the material which is softened by the rotationof the rotary tool 70. For example, the material of the raised portion32 of the frame member 30 is moved in above-stated gap and the gap isfilled in by this material.

[0042] From the tip end of the small diameter portion 72 of the rotarytool 70, a softened material is moved to a lower portion of the gap, andthen the gap is filled in by the softened material. As a result, thelower boundary of the gap (at the lower end of the frame members 30) isformed substantially in the same plane as the outer face 31 c of theplate 31 of the frame member 30. The reference numeral 36 in FIG. 5indicates a welding bead which is formed to fill this gap.

[0043] Since the outer face of the welding bead is formed substantiallyin the same plane as the outside face 31 c of the frame members 30, thethickness of the putty used during the welding can be made thin.Further, since there is a raised portion 32 on the outer face on whichthe bead 36 does not exist, it can be finished using the hair lineprocessing having no coating.

[0044] Accordingly, an assembly of the welded frame members 30 and anassembly of the two extruded frame members 40, arranged as seen in FIG.6, are mounted on and fixed to the stand 60, as shown in FIG. 1. Inadvance, the rib 43 of the frame member 40 in the vicinity of thewelding portion (at both ends of the frame member 40) is cut off, sothat the end surfaces of this extruded frame member 40 are formedsmoothly. As a result, when the above-stated welding in this embodimentis carried out according to the friction stir welding method, the areain the vicinity of the welding portion can be pressed by rollers intofirm contact with the stand 60, as mentioned above.

[0045] Next, as seen from FIG. 1 to FIG. 3, at the abutting portions(the welding portions) of the two assemblies, a welding pad is providedalong the end portions of the extruded frame members 40. It is desirableto provide welding pads 42 having a height and a width which correspondsto the height and a width of the raised portion 32 of the frame member30. For this purpose, it is desirable to dispose a continuous weldingpad along to the welding line, but it is also possible to provideintermittently disposed welding pads. For example, the individualwelding pads may be about 1 cm in length and be disposed at about 1 cmintervals along the welding line. The strength of these welding pads hasto be sufficient that, during the friction stir welding, the material isnot thrown out by the rotating action of the rotary tool 70. Anallowance will be permitted for the fact that the large diameter portion71 of the rotary tool 70 will cause the material to be thrown up; sincethis facilitates the formation of the recessed portion 35.

[0046] As stated above, the friction stir welding is carried out on theframe members 30 and the extruded frame members 40 such that the outerfaces 31 c and 41 c of the plates 31 and 41 are aligned substantially inthe same plane.

[0047] When there is no welding pad portion 42, since the large diameterportion 71 and the small diameter portion 72 of the rotary tool 70 cannot extend sufficiently into the extruded frame member 30 and theextruded frame member 40, the material of the raised portion 32 issplashed out and the filling of the material into the gap becomesinsufficient. As a result, a good welding of the extruded frame member30 and the extruded frame member 40 can not be obtained. However, inthis embodiment according to the present invention, since the weldingpad portion 42 on the frame member 40 serves to supplement the raisedportion 32 of the frame member 30, a good welding can be carried out onthe extruded frame member 30 and the extruded frame member 40.

[0048] The welding pad portion 42 is formed intermittently in thisembodiment according to the present invention; however, material willmove from the raised portion 32 of the frame member 30 to the side ofthe frame member 40 during welding. Further, in response to the rotationand the movement of the rotary tool 70, the materials of the raisedportion 32 and the welding pads 42 are moved toward a rear portion ofthe rotary tool 70. As a result of such movement of material along thewelding line, a good welding where no welding pad 42 exists can besubstantially achieved.

[0049] The welded portion in this case becomes substantially as shown inFIG. 5. The remnants of the raised portion 32 of the extruded framemember 30 are provided on one side of the welded portion and theremnants of the welding pad portions which form the raised portion ofthe extruded frame member 40 are provided on the other side of thewelded portion.

[0050] When the outer face of the car panel is finished withoutpainting, the above stated welding of the pads is carried out accordingto the TIG welding method. The filler material is the same material asthe frame members 30 and 40. In this regard, by cutting the framemembers 30 and 40, the filler material is provided. For example, the endmaterials of the frame members 30 and 40 may be used for the fillermaterial. According to this embodiment, there is no change of color atthe welding portion, so that a nice appearance can be obtained. When thefiller material is another material, a change of color appears at thewelding portion and a nice appearance can not be obtained.

[0051] In the above stated embodiment according to the presentinvention, after welding the pads, the frame members may be installed onthe stand 60 to form the panels. In the above stated embodiment of thepresent invention, the welding of the extruded frame members to eachother is effected for constituting the side structure body, however suchwelding techniques can be used to join other members as well.

[0052] Another embodiment according to the present invention will bedescribed with reference to FIG. 7 and FIG. 8. An extruded frame member80 is arranged in longitudinal direction of a car body. The extrudedframe member 80 is a hollow-shaped frame member made of an aluminumalloy material. A raised portion is formed at both faces of the endportions in a width direction of the extruded frame member 80. Thewelding of the frame members 80 to each other is carried out using thefriction stir welding method by utilizing the raised portion to supplymaterial to the weld.

[0053] The reference numeral 86 identifies a window and the referencenumeral 87 identifies a doorway. Reference numerals 90 and 95 areextruded frame members for constituting a frame of the doorway 87. Theframe member 90 constitutes a vertical side frame member and the framemember 95 constitutes an upper side and a lower side frame member. Theextruded frame members 90 and 95 are welded to each other according tothe friction stir welding method. The frame formed by the extruded framemembers 90 and 95 and the extruded frame member 80 are also welded toeach other according the friction stir welding method. The frame member90 is a hollow-shaped frame member made of an aluminum alloy material.

[0054] Raised portions 92 are provided at both faces at adjacent cornerportions of the frame member 90. Further, projecting chips 93 whichproject toward the frame member 80 are provided. The projecting chips 93are inserted into the hollow interior of the two plates 81 and 82 of theframe member 80.

[0055] In the frame member 80, the inner rib 83 is deleted—or cut off toaccommodate the insertion of the projecting chip 93. According to thewidth of the vertical side 91 of the frame member 90, an abutting facebetween the raised portion 92 and the frame member 80 is provided. Theconstruction of the frame member 95 is the same as the construction ofthe frame member 90. The two plates 81 and 82 of the frame member 80 arearranged substantially in parallel.

[0056] After the frame members 80 have been joined by friction stirwelding, the frame members 90 and 95 are joined. Then, the frame members80, 90 and 95 (excluding the raised portion 92) are mounted on the stand60. Along the frame members 90 and 95, and to end portions of the framemembers 80, the welding of the pads is carried out. After that, thefriction stir welding to join the panels formed by frame members 80 tothe frame formed by frame members 90 and 95 is carried out.

[0057] The friction stir welding is carried out on one face at a time oris carried out simultaneously on both faces. After the friction stirwelding, the remnants of the raised portions on the outer side of therailway vehicle and the remnants of the welding pads are cut off, andthen the outer side of the railway vehicle is formed smoothly.

[0058] The above-stated embodiment according to the present inventioncan be applied to a case in which the frame of a window is installedusing the friction stir welding method. Further, in the above statedembodiment, a hollow-shaped frame member is adopted, but the framemember shown in FIG. 1 can be used instead.

[0059] In the above stated embodiment according to the presentinvention, when members having a different thickness at the end thereofare abutted, such as might occur as a result of a manufacturing error,so that the height of the surface of the welding portion is not uniform,the use of welding pads may be employed for the member at the low side,after which the friction stir welding can be carried out.

[0060] Further, the indication that “the height of the surface of thewelding portion is not uniform” refers to a case in which it is assumedthat the surface portion on one side of the welding line is higher thanthe other, for example; however, when the rotary tool is standard, forexample, it means that the distance from the rotary tool to the surfaceon either side of the welding line differs. The reference to “the memberat the low side” indicates a member which is at a greater distance fromthe rotary tool.

[0061] A further embodiment will be explained with reference to FIG. 9.The structure shown in FIG. 9 substantially corresponds to that of FIG.8. In this embodiment, both the rib 83 of the end portion of the hollowframe member 80 and the end portion of the plate 82 of the inner side ofthe car body are cut off and removed. An end portion of an outer side ofan extruded frame member 100 is abutted to the plate 81. To this endportion of the extruded frame member 100, a raised portion 102 isprovided, and this raised portion 102 is projected toward the outer sideof the car body.

[0062] An outer face of the extruded frame member 100, excluding theraised portion 102, and the outer face of the plate 81 are arranged tobe substantially in the same plane. A projection chip 103 of a face onthe inner side of the car body on the extruded frame member 100 isoverlapped on the plate 82 of the extruded frame member 80. The extrudedframe member 100 is not a hollow-shaped frame member, but is solid toprovide increased strength.

[0063] When the solid extruded frame member 100 has been mounted on thestand 60 in engagement with the frame member 80, the abutted portionbetween the plate 81 and the extruded frame member 100 is subjected tofriction stir welding from an upper position. The friction stir weldingmethod is carried out using the raised portion 102 to provide materialfor the weld. Next, the structural body is turned over, and then theprojection chip 103 and the plate 82 are fillet welded using arcwelding. Further, in a case where there is no projection chip 103, theabutted portion between the plate 82 and the extruded frame member 100is welded.

[0064] The technical scope of the present invention is not limited tothe description provided in this specification, but can cover a range inwhich a man of ordinary skill in this field easily understand from thedescription.

[0065] According to the present invention, in the case where the heightof the surfaces of two members at welding portion differs, a goodwelding of the two members can be obtained.

What is claimed is:
 1. A car body comprising: an end portion of a first member abutting and welded to an end portion of a second member, each of the first and second members being extruded frame members, an extruding direction of said first extruded frame member and an extruding direction of said second extruded frame member being substantially orthogonal; a welded portion which protrudes from said first extruded frame member and said second extruded frame member in a thickness direction thereof, a central portion of said welded portion in a width direction being recessed; said welded portion including a first protruding portion which is derived from said first extruded frame member, and a second protruding portion which is derived from a padding welded on said second extruded frame member; and said extruded portion being disposed on an inner side of the car body.
 2. A car body according to claim 1, wherein: said first extruded frame member is formed by welding plural extruded frame members; said second extruded frame member is formed by welding plural extruded frame members; an end portion of a first assembly of said plural first extruded frame members and an end portion of a second assembly of said plural second extruded frame members are welded to form said welded portion; and said first and second assemblies exist in a side body portion of said car body.
 3. A car body according to claim 2, wherein: said second assembly forms at least a part of a doorway or a frame of a window. 